STRUCTURE OF THE EXOCRINE PANCREAS OF FLOUNDER (PARALICHTHYS-OLIVACEUS) - IMMUNOLOGICAL LOCALIZATION OF ZYMOGEN GRANULES IN THE DIGESTIVE-TRACT USING ANTI-TRYPSINOGEN ANTIBODY

Most fish have a diffuse exocrine pancreas located around the internal organs, but its exact structure is not well understood. In this study, we developed a method for analysing zymogen granules using anti-fish trypsinogen, and the structure of the flounder pancreas was examined by localizing pancreatic exocrine cells. Anionic trypsinogen was purified from eel pancreas by chromatography using DE-52-cellulose and Superose 12 columns. Rabbit antiserum (anti-eel trypsinogen antibody: anti-eTrg) was raised against purified trypsinogen. Immunoblotting analysis demonstrated that anti-eTrg recognized two isoforms of eel trypsinogens and trypsins. This antibody also reacted with flounder trypsin. Zymogen granules containing trypsinogen were visualized within pancreatic glandular cells of the flounder Paralichthys olivaceus by immunohistochemistry using anti-eTrg. The flounder exocrine pancreas was reconstructed from observations of serial sections of digestive tract. The exocrine pancreas cells were localized along the hepatic portal vein and the veins running to the portal vein from the intestine, stomach, pyloric appendage and spleen, forming a highly branched tissue. Interlobular ducts from pancreatic acini formed a pancreatic duct covered with smooth muscle at the point where it met (but did not join) the bile duct. The pancreatic duct opened into the intestinal lumen at the basal portion of the third pyloric appendage in parallel with the bile duct.